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This research examines whether individual exposures to traffic congestion are significantly different between assessments obtained with and without considering individuals' activity-travel patterns in addition to commuting trips. We used crowdsourced real-time traffic congestion data and the activity-travel data of 250 individuals in Los Angeles to compare these two assessments of individual exposures to traffic congestion. The results revealed that individual exposures to traffic congestion are significantly underestimated when their activity-travel patterns are ignored, which has been postulated as a manifestation of the uncertain geographic context problem (UGCoP). The results also highlighted that the probability distribution function of exposures is heavily skewed but tends to converge to its average when individuals' activity-travel patterns are considered when compared to one obtained when those patterns are not considered, which indicates the existence of the neighborhood effect averaging problem (NEAP). Lastly, space-time visualizations of individual exposures illustrated that people's exposures to traffic congestion vary significantly even if they live at the same residential location due to their idiosyncratic activity-travel patterns. The results corroborate the claims in previous studies that using data aggregated over areas (e.g., census tracts) or focusing only on commuting trips (and thus ignoring individuals' activity-travel patterns) may lead to erroneous assessments of individual exposures to traffic congestion or other environmental influences.

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1467-9272.2007.00633.x Byline: Mei-Po Kwan (1) Keywords: activity patterns; mobile communications; social networks; spatial interaction; urban travel Abstract: The widespread use of mobile communications is leading to new practices in family life and social life, and these changes have significant implications for the study of urban travel. Because of the adoption of new modes of space-time coordination, changing time use and increasing mobility, changing use of existing urban nodes, the blurring of boundaries between home and work, the importance of social networks and social capital, and the shift to person-to-person connectivity, the spatial structure and processes of interaction among individuals have become much more complicated in this age of mobile communications. Static spatial frameworks based on fixed points (e.g., home or workplace) and distances among them are no longer adequate for understanding urban travel. The study of urban travel now needs new conceptualizations and new methodologies. Author Affiliation: (1)The Ohio State University Article History: Initial submission, March 2006; revised submission, November 2006; final acceptance, April 2007.

Analytical methods for evaluating accessibility have been based on a spatial logic through which the impedance of distance shapes mobility and urban form through processes of locational and travel decision [...]

Although recent studies of individual accessibility have used detailed representations of urban street networks, unrealistic measures of travel time based on assumptions about constant travel speeds through the network were often used. Utilizing constant travel times does not allow for daily congestion and assumes that the effects of congestion are uniform throughout the city and affect all people equally. This research measures individual space-time accessibility in order to show that the incorporation of locally specific travel times within a street network allows a significant increase in the ability to realistically evaluate individual accessibility within cities. The results show that the accessibility of individuals within cities is not homogenous, and neither does access to employment or shopping opportunities vary according to common expectations about urban form and human behavior. Instead, the role of distance in predicting accessibility variations within cities is quite limited. This article also shows that incorporating time into accessibility measures in the form of congestion and business hours leads to additional (and highly spatially uneven) reductions in accessibility, revealing that the temporal dimension is very important to accurately assessing individual accessibility. Key Words: accessibility, geographic information systems, time.

Accessibility to various utilities in a town or city has always influenced the decision of residents to set up residence in a particular area or district. A research was conducted to evaluate the importance of geographic context within the urban environment for residents of Portland, Oregon.

This study examined how contextual areas defined and operationalized differently may lead to different exposure estimates. Substance users' exposures to environmental stress (in terms of two variables: community social economic status and crime) were assessed from global positioning systems (GPS) data. Participants were 47 outpatients with substance use disorders admitted for methadone maintenance at a research clinic in Baltimore, Maryland. From 35.2 million GPS tracking points, we compared 7 different methods for defining activity space. The different methods yielded different exposure estimates, which would lead to different conclusions in studies using only one method. These results have important implications for future research on the effect of contextual influences on health behaviors and outcomes: whether a study observes any significant influence of an environmental factor on health may depend on what contextual units are used to assess individual exposure. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses articles in the issue on the topic of uncertainties in geographic information science (GIScience) and geography caused by errors in geospatial data measurement.

The various books on information technologies by geographers and the relation between them are reviewed. Three related perspectives and areas of research whose relevance and value to IT-related research in geography is relatively unnoticed to date are focused.

Conventional accessibility measures based on the notion of locational proximity ignore the role of complex travel behavior and space-time constraints in determining individual accessibility. As these factors are especially significant in women's everyday lives, all conventional accessibility measures suffer from an inherent 'gender bias.' This study conceptualizes individual accessibility as space-time feasibility and provides formulations of accessibility measures based on the space-time prism construct. Using a subsample of European Americans from a travel diary data set collected in Franklin County, Ohio, space-time accessibility measures are implemented with a network-based GIS method. Results of the study indicate that women have lower levels of individual access to urban opportunities when compared to men, although there is no difference in the types of opportunities and areas they can reach given their space-time constraints. Further, individual accessibility has no relationship with the length of the commute trip, suggesting that the journey to work may not be an appropriate measure of job access. Key Words: accessibility, gender, space-time constraints, urban opportunities.

This article introduces the background and contents of this forum, which includes six articles based on presentations in the opening and closing plenary sessions of the featured theme on “Context and Uncertainty in Geography and GIScience” at the 2017 American Association of Geographers (AAG) annual meeting in Boston. The purpose of the featured theme was to explore and deepen our understanding of the spatiotemporal uncertainties in the contextual influences on human behavior, practice, and experience. The articles in this forum focus on specific themes concerning context and uncertainty in geographic and GIScience research. They provide a helpful discussion of the complexity and challenges of specific issues through different theoretical and methodological perspectives. [ABSTRACT FROM AUTHOR]

Accompanied by higher levels of car ownership, suburbanisation in Western countries has a significant impact on motorised travel and long-distance trips. Chinese cities share some of the suburbanisation trends and patterns of the United States as well as an increasing number of cars, while there are still great contextual variations. Through a comparative study of activity space in two inner suburban areas with different built environments, Beijing in China and Chicago in the US, this paper examines how suburbanisation influences individuals’ activity-travel behaviour. The results indicate that changing urban form has a significant impact on activity space. However, the determinants of activity space in Beijing are quite different from those in Chicago. In Beijing, increasing car ownership leads to more differentiation among suburban residents. In Chicago, encouraging high-density land use patterns may lead to more localised activity space. [ABSTRACT FROM AUTHOR]

Increasingly, ‘place’, including physical and geographical characteristics as well as social meanings, is recognized as an important factor driving individual and community health risks. This is especially true among marginalized populations in low and middle income countries (LMIC), whose environments may also be more difficult to study using traditional methods. In the NIH-funded longitudinal study Mapa de Salud, we employed a novel approach to exploring the risk environment of female sex workers (FSWs) in two Mexico/U.S. border cities, Tijuana and Ciudad Juárez. In this paper we describe the development, implementation, and feasibility of a mix of quantitative and qualitative tools used to capture the HIV risk environments of FSWs in an LMIC setting. The methods were: 1) Participatory mapping; 2) Quantitative interviews; 3) Sex work venue field observation; 4) Time-location-activity diaries; 5) In-depth interviews about daily activity spaces. We found that the mixed-methodology outlined was both feasible to implement and acceptable to participants. These methods can generate geospatial data to assess the role of the environment on drug and sexual risk behaviors among high risk populations. Additionally, the adaptation of existing methods for marginalized populations in resource constrained contexts provides new opportunities for informing public health interventions. [ABSTRACT FROM AUTHOR]

Drawing on examples from human mobility research, I argue in this article that the advent of big data has significantly increased the role of algorithms in mediating the geographic knowledge production process. This increased centrality of algorithmic mediation introduces much more uncertainty to the geographic knowledge generated when compared to traditional modes of geographic inquiry. This article reflects on important changes in the geographic knowledge production process associated with the shift from using traditional "small data" to using big data and explores how computerized algorithms could considerably influence research results. I call into question the much touted notion of data-driven geography, which ignores the potentially significant influence of algorithms on research results, and the fact that knowledge about the world generated with big data might be more an artifact of the algorithms used than the data itself. As the production of geographic knowledge is now far more dependent on computerized algorithms than before, this article asserts that it is more appropriate to refer to this new kind of geographic inquiry as algorithm-driven geographies (or algorithmic geographies) rather than data-driven geography. The notion of algorithmic geographies also foregrounds the need to pay attention to the effects of algorithms on the content, reliability, and social implications of the geographic knowledge these algorithms help generate. The article highlights the need for geographers to remain attentive to the omissions, exclusions, and marginalizing power of big data. It stresses the importance of practicing critical reflexivity with respect to both the knowledge production process and the data and algorithms used in the process. [ABSTRACT FROM AUTHOR]

This introductory piece sets the context for the special issue and explains its rationale. It offers a series of reflections on the rise of the mobilities turn and its relations with preexisting research traditions, most notably transportation geography. Rather than placing different approaches in opposition and favoring one over others, we contend that all need to be seen as situated, partial, and also generative modes of abstraction. Each of these approaches makes mobility exist in specific and ultimately simplified and selective ways. In addition, we argue that geography as a pluralistic discipline will benefit from further conversations between modes of conceptualizing, theorizing, and examining mobility. We outline five lines along which such conversations can be structured: conceptualizations and analysis, inequality, politics, decentering and decolonization, and qualifying abstraction. The article concludes with discussion on three fruitful directions for future research on mobility. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigate the intra-personal day-to-day flexibility of commuting behavior. [•] A 7-day GPS dataset collected in Beijing, China and 3D geovisualizations were used. [•] 7 commuting patterns based on space, time, travel mode and route were identified. [•] The results show that the commute trip is flexible and complex in many ways. [•] They call into question the assumption that the commute trip is stable and fixed. [Copyright &y& Elsevier]

The uncertain geographic context problem (UGCoP), first articulated by Kwan (2012; The uncertain geographic context problem. Annals of the Association of American Geographers, 102 (5), 958–968), refers to the problem that findings about the effects of area-based contextual variables on individual behaviors or outcomes may be affected by how contextual units (e.g., neighborhoods) are geographically delineated and the extent to which these areal units deviate from the true geographic context. It is a significant methodological problem because it means that analytical results can differ for different delineations of contextual units even if everything else is the same. Drawing upon Kwan (2012) and recent social science studies (especially environmental health and neighborhood effects research), this article further elaborates on the nature of the UGCoP and explores how recent advances in geographical information system (GIS) and geospatial technologies can help address the problem. It discusses possible means for mitigating the UGCoP, especially with regard to the collection of detailed individual space–time data with global positioning systems, construction of individual activity spaces, and the use of qualitative and web-based GIS to capture people's activity locations and everyday experiences. It also discusses the challenges for future research that seeks to address the UGCoP. [ABSTRACT FROM AUTHOR]

Criticisms of quantitative geography have a long history in our discipline. Since the emergence of early Marxist geography, the advent of new theoretical traditions has been accompanied by sustained and sometimes vigorous critiques of spatial analysis. In this introductory article to the second focus section on critical quantitative geographies, we discuss the accuracy of some of the criticisms about the use(s) to which spatial analysis is put and about the philosophical presumptions underpinning quantitative geographies. We argue that spatial analysis and critical geographies should not be considered mutually exclusive of one another—although this does not mean that numbers and critical geographies are entirely comfortable with one another. We suggest that critical geographies cannot dispense with numbers and visualizations based on numerical information. We hope that the articles collected here will inspire geographers to engage with numbers and statistics to challenge inequality and imagine alternative futures. [ABSTRACT FROM AUTHOR]